Moves on how to handle use-of-force cases follow controversies over killings of black men

Prosecutors across the country are looking for new ways to handle police use-of-force cases.

In Maryland, Baltimore State’s Attorney Marilyn Mosby is pushing for state legislation to give police powers to her investigators. San Francisco District Attorney George Gascón is creating a unit to lead police-shooting investigations, instead of having the police take the lead. In November, the Philadelphia district attorney introduced a policy to send staff attorneys to any police shooting.

The moves follow a string of failed prosecutions in cases involving fatal police shootings of black men, and several controversial decisions not to prosecute, such as in Charlotte, N.C., and Ferguson, Mo. Given their close day-to-day work with law enforcement, district attorneys can face criticism for not holding police accountable. Prosecutors, meanwhile, say it is more complicated than that; they have to assess each case on its merits and consider how a jury—often sympathetic to police—would decide.

“We’ve let a lot of this debate fall on the back of police and on the back of communities who have been upset, and we have not stepped up and taken our proper role,” said Jean Peters Baker, chief prosecutor in Jackson County, Mo., in the Kansas City area. “We’ve lost public trust because people couldn’t see what we did or why.”

Since a grand jury declined to indict the Ferguson officer who fatally shot Michael Brown in 2014, Ms. Baker, in use-of-force cases, typically bypasses grand juries and instead relies on senior prosecutors to help her decide whether to charge officers. Ms. Baker said she wants to better explain the reasons if no charges result.

The grand-jury process “has real limitations on what we are allowed by law to tell the public,” she said. Grand juries, which meet behind closed doors, don’t determine guilt, they only decide to move forward with a trial.

Since 2014, eight states have made changes to the process of investigating officer-involved deaths or alleged police abuse, according to the National Conference of State Legislatures. Connecticut mandates that a state agency investigate use-of-force cases, while Illinois, Utah and Wisconsin require the use of outside investigators.

Jeffery Robinson, deputy legal director at the American Civil Liberties Union, praised the steps being taken, “but I am not on this bandwagon of, ‘Hey, these are radical changes that are great,’ ” he said. “My view is, what took us so long?”

Jim Pasco, executive director of the national Fraternal Order of Police, said he doesn’t object to some steps being advocated, such as sending a prosecutor to police shooting scenes.

“As long as they do their investigation with principle and reverence for the law, we have no problem,” Mr. Pasco said. He said it makes sense for outside police agencies to lead investigations involving law-enforcement officers, though some police departments say that isn’t practical.

Since 2015, 31 officers involved in fatal on-duty shootings have been charged with murder or manslaughter, compared with 48 the prior decade, said Philip Stinson, a criminologist at Bowling Green State University in Ohio. Even so, Mr. Stinson notes the vast majority of the roughly 1,000 fatal shootings by police each year don’t result in prosecution.

The topic will be raised at an annual meeting of prosecutors this week in San Francisco, where a raft of new initiatives is expected to be discussed that aim to improve transparency, procedural fairness and accountability on the part of prosecutors.

Meanwhile, in Philadelphia, District Attorney Seth Williams began sending his staff attorneys out to police shooting scenes, a longstanding practice elsewhere, including the Los Angeles County District Attorney’s Office. Mr. Williams also plans to meet with relatives of those killed by police at the start and end of investigations, and to publicly detail his ultimate decision.

The city is no stranger to fatal police shootings. In 2013 the police department asked the U.S. Justice Department to help it address a rise in such shootings. Earlier this month, federal officials praised the Philadelphia police department’s steps, including the creation of a unit to probe all deadly force incidents. The number of lethal police shootings dropped to five last year after reaching 16 in 2012.

Since introducing the new protocol in November, Mr. Williams’s office said it has investigated one fatal police shooting in Philadelphia, two nonfatal shootings by Philadelphia police and two incidents in which city officers shot dogs.

Mr. Williams said that while he doesn’t lack confidence in the police department’s ability to investigate its officers, the public needs greater assurances.

“I wanted the public to know we’re not just rubber-stamping the police investigation,” he said. “We’re just one catastrophe away from what happened in Ferguson,” he added.